Altimeter for obtaining actual altitude of aircraft



Nov. 7, 1944. w. NAIDA ALTIMETER FOR OBTAINING ACTUAL ALTITUDE OF AIRCRAFT Filed Oct. 28, 1942 IMIP W Z i/IZZIZTOR.

' tion due to varying relative air velocity.

Patented Nov. 7, 1944 UNITED :STATES PATEN T OFFICE ammo FOR OBTAINING ACTUAL ALTITUDE or AIRCRAFT William N aida,

New York, N. Y., assignor oi one-half to Emilio Van-one, Brooklyn. N. Y. Application October 28, 1942,8613! No. 463,715

4 Claims. (0]. 73387) This invention relates to indicating instruments for aircraft and to devices for the"comparative indication of dynamic conditions of the flow of gases. I

One object of the invention is to provide an altimeter having improved air-sensitive means for indicating the substantially, true altitude of I an aircraft in flight, irrespective of a sudden drop in barometric pressure such as occurs in the case of a storm or other unusual condition.

Another object of the invention is to provide an improved altimeter responsive to dynamic air Y of an improved altimeter wherein aneroid means are used for indication of altitude as well as for correction or modification of vertical dynamic energy indication for diflerent densities of the air as distinguished from dynamic energy varia- Another object 01' the invention is to provide an altimeter having improved means for indicating the resultant change in altitude as between the climbing of an aircraft and the effect of a sudden drop in barometric pressure.

Another object of the invention is to provide an altimeter having improved means including indicating means for the reading du to normal pressure, the resettable rea ing due to the loss of altitude of the. aircraft during a sudden drop in barometric pressure, and the resultant substantially true altitude reading, each of these readings being constantly'shown, simultaneously with the others;

Another object of the invention is to provide an altimeter having improved means whereby the size of scale readings for certain altitude ranges is changed by improved simplified mechanism.

Another. object of the invention is to provide improvements in the art relating to the observation of certain physical characteristics of gases, particularlypressure and dynamic energy, including conditions encountered in the atmosphere by aircraft, applicable not only to altimeters' but as an aneroid in association with enhance the dynamic ceeds.

also to many other devices and for diiferent purposes, comprising the following:

1. To utilize a Pitot tube for dynamic indication.

2. To employ a Venturi .tube for control of dynamic energy, as a means of adjustment, and forother purposes.

3. To coordinate streamlined means with an indicator of one component of dynamic energy so as to obtain, for example, an indication of vertical air flow independently of horizontal air flow, of a mass of air.

.4. To combine a venturi with a Pitot tube to energy available for easier energy relative indication.

5. To movably associate a venturi with a Pitot tube for adjustment or the indication of the latter.

6. To use a venturi with a Pitot tube movable by a pressure sensitive device such as an aneroid for changing the indication of the latter in accordance with variation in the air density.

7. To employ a pressure sensitive device such means for dynamic energy indication to impose a force or eil'ect modifying said indication in direct or in-- verse proportion to varying sas density.

a. To obtain the resultant eflect between vet-- tical upward and thus allow for a density change efl'ects.

9. To change the speed of operation or.of indication of a timing device such as a clock. according to the dynamic energy of a gas, or according to such a condition together with the varying density of the gas; and to accomplish this bya single movement, with the aid; for instance, of a governor. y

10. To afiect the rate of a time mechanism according to atmospheric conditions as herein mentioned, without drawing power from an aneroid, or the like.

-11.'To cause an indicator for the drop of an aircraft to begin to operat automatically and to cease operation when the drop ceases, and to be adapted to be reset to zero.

Other objects and advantages of the invention will become apparent as the specification prodownward relative air now to With the' aforesaid objects in view, the inventiOn consists in the novel combinations and arrangements of .parts hereinafter described in their-preferred embodiments, pointed out ;in the subjoined claims, and-illustrated on the annexed drawin wherein like parts are designated by the combination of movement and same reference characters throughout the several Fig. 2 is a view in elevation. showing the dial face of the device.

Fig. 3 is a modification.

Fig. 4 is a view of the device including mechanism for changing the speed of the pointer according to a change in the scale divisions.

The advantages of the invention as here outlined are best realized when all of its features and instrumentalities are combined in one and the samestructure, but, useful devices may be produced embodying less than the whole.

It will be obvious to those skilled in the art to which this invention appertains, that the same may be incorporated in several different constructions. The accompanying drawing, therefore, is submitted merely as showing the preferred exemplification of the invention.

Referring in detail to the drawing, I! denotes a device or system embodying the invention, examplified in an altimeter, though certain principles thereof are applicable for other devices and purposes. The same may include a casing or support i l which may be mounted pendulously or by universal means such as gimbals, illustratively indicated by the pivot 12. A pressure sensitive device such as an aneroid I2 is fixedly centrally mounted in the casing as on a supporting element l4. Coaxially connected to the opposite side of the aneroid is a link it. Pivotally connected to the latter at I is the arm I! of a segmental gear I! having a fixed shaft at 19. Engaging the gear I is a pinion having a fixed axis and serving to rotate an indicator element such as a pointer 2|. The altimeter thus constructed, when provided with a scale, forms the usual device heretofore known, and maybe compensated for temperature changes, lag or specific hysterisis, counter-balanced as to certain moving parts, and provided with other refinements well known in the art, and which need not be shown herein.

Also provided in the casing H is a Venturi tube 22 whose mouth, or entrance 22 faces downward, and the axis whereof is vertical. This venturi may have a relatively long throat 24 to equalize the velocity therein and to cause emcient transformation of velocity head into pressure head in the large cone of the venturi., This transformation occurs gradually so that turbulence is reduced to a minimum. For these purposes the length of the cylindrical portion 24 is between four and six times the internal diameter. If desired, a second Venturi tube 25 like that at 22. but in inverted relation thereto may be provided. Both Venturi tubes may project from the casing H at holes 28 so that the mouths thereof are wholly exposed for the flow of air thereinto, and these tubes may be secured to the casing at 2!.

To avoid eddy currents at the entrances of the Venturl tubes, and cause the how thereinto of air actuated by the vertical component of a relatively angular current of air. I provide rectifying means such as 21. The latter may consist of streamlined elements adapted to produce the same amount of pressure at their upper surfaces as at their lower surfaces, so as to afford a neutral or balanced result which shall not affect the Venturi tubes. Illustratively, each element 21 may be of horizontal disc form with upper and lower convexly curved surfaces. Each may have a central vertical opening 28 for receiving the entrance 22 of a Venturi tube with ample clearance, said entrance lying about in the central horizontal plane of the element 21. Each of the latter' may be fixedly mounted as by arms or struts 29 connected to any adjacent stationary part in a manner such that wind resistance may be reduced to a minimum. It will be appreciated that the casing ll may also be so mounted or streamlined as to afford the desired minimum air resistance, and may have suitable openings such as Ila so that the air may flow out of the ,casing. Y

Within the expansion cone of each Venturi tube 22 and 25 are axially disposed Pitot tubes 20, 3| whose small ends point toward the cylindrical portions 24 and may lie where the cone begins or within the cylindrical portion, provided that they do not upset the uniform velocity condition sought to be obtained in the portions 24. In this regard, the diameter of the portions 24 must be considered, since a reduction in diameter would substantially increase the effect of the Pitot tube as an obstruction and resistance factor. The shape of the Pitot tube is another factor, and in general it is possible to select various pointsas above indicated at which the fine end of the Pitot tube may lie. The purpose of the Venturi tube is to increase the dynamic energy of the air or at least to afford the maximum of such energy so that suflicient power may be derived from the Pitot tube for actuation of an instrument. The venturi also afiords a uniform stream of air for the Pitot tube. And the venturi has still a further function of sewing as a control or adjusting element for the Pitot tube, since each of the latter is slidably mounted as in stationary guides 32 for vertical reciprocation as hereinafter described. It will be evident that as the Pitot tube is retracted so that its point enters the expansion cone of its venturi, the dynamic energy of the air diminishes, and the Pitot tube indicates a, reduced velocity head. By associating suchan adjustable action with a. pressure sensitive device. such as an aneroid, a novel principle is realized because the aneroid can cause retraction of the Pitot tubes in proportion to its contraction It is well known that the velocity head in the expansion cone of the venturi becomes progressively less toward its outlet, while pressure head increases: hence the Pitot tube pressure diminishes upon retraction. A drop of an aircraft under given conditions, in the case of a storm as mentioned, would cause a substantially higher pressure in a Pitot tube, at relatively low altitudes, than the same drop at high altitudes because the air has less density in the latter case. Hence the Pitot tube pressure might be considered to show that the drop in the former instance is much greater than is actually true. Consequently for the lower altitudes the relatively contracted aneroid has retracted the Pitot tube to a suitable point from the cylindrical section of the venturi, at which point a lower velocity head prevails, to cause a reduced Pitot tube pressure, so that the pressure at the relatively low altitudes shall be consistent with those at the high altitudes, for the conditions above stated. Thus the varying density of the air is substantially eliminated as a factor.

A diiferent or the same aneroid 13 may be used to actuate the Pitot tubes. For example, a plurality of levers may be used, with any desired leverage according to the relative motion desired mally maintained in a correspondingly greater or less.

as between the aneroid and the tubes. It may be desirable to cause a greater motion for the tubes than the expansion of the aneroid. Hence a lever 33 having a fixed pivot at 34 may be connected by a link 35 to a substantially central point of the aneroid, adjacent to the link l5. Pivotally connected to the lever 33 at 33 is a lever 31 having a fixed Divot at 38. nected to the pivot element33, and the tube 3] is connected .to the lever 31 by a pivot element 39. Suitable lost motion may be provided where necessary for operation of the levers, and counterbalancing means may be aflorded where desirable, but these elementary matters need not be discussed in detail herein.

To transform the energy obtained from the Pitot tubes into mechanical power, a diaphragm or piston 43 is employed in a casing 4 I. The area of piston is as large as may be required to obtainthe necessary power. This piston may be norgiven or central position, as by opposed, relatively weak, expansion coil springs 42 which are mounted, for instance, on the piston rod 43. The Pitot tubes 33 and 3| are connectedto the casing 4| at opposite sides of the piston by pipes 44, 45. For this purposethe portions 44a and 45a of the levers 33 and 31 may be tubular, and the pivots at 34, 33, 33 and 33 may also be tubular, all so arranged as to alf ord continuous conduits from the Pitot tubes. It will now be apparent that the piston 43 will move according to the differential pressure, against the force of one or the other of the springs.

By means of piston 43 the tained of conditions where there is a sudden drop in barometric pressure so that the altitude of an aircraft diminishes and then the pilot causes the aircraft to climb to overcome the loss of altitude mentioned.

Movement of the piston to the right or left of neutral initiates operation of a suitable clock or time mechanism, which may comprise a source of power such as a spring woundmotor 43 actuating a gear 41 which engages a pinion 43 fixed to the gear 43, the latter engaging a gear 53 to which is secured a bevel gear 5| thatis in engagement with a like gear 52. Rotation of the latter causes operation of any suitable escapement or speed control or regulator device 53 herein schematically shown, whereby operation at constant speed.

is obtained. To vary the constant speed anysuitin whole or in part The Pitot tube 33 is conable governor 54, schematically shown,-is' "connected by means of a beveled pinion to the gear 52. Controlling the governor 54 is a cam means 53 or other device aflixed which may have a bearing at 51. The cammeans may include two aligned coneswhose small ends gear train will Operated by the gear train is a gear driver 53 for a pointer, dial or other indicator element. This gear 58 may be releasably engaged with the said gear train by a movable gear 53 or by a movable gear 33, whose movement is responsive-to the piston 43 as hereinafter described. The gear 53 may be engaged with a gear 3|; both gears 53'and 3| are engaged'with a large gear 32 that engages the pinion 48. It will now to the piston rod 43,

be Seen that the gears with the gear 53. In operation of the gears is in engagement 3 53 and v33 rotate in opposite directions, so that the gear 53 rection depending upon which of the gears 53 and 33 engages the gear 53. It will be appreciated as the description proceeds that one of the gears Y53 and 33 may be omitted, as it will sumce that the indicator element turned by the driver 53 shall rotate in only one direction. It is to be noted that the gearing and gear ratios herein shown are merely illustrative or suggestive and may be modified to suit. I

Controlling themovement of the gears and 33 are the solenoids 33, 34 which are fixedly mounted and are provided with cores operatively mounting the gears so that they remain constantly in engagement with their respective gears 32 and 3|, and yet are movable into engagement with the gear 53. If both solenoids are deenergized, both of the gears 53 and 33 may be moved into engagement with the gear 53 whereby the gear train becomes locked and automatically stops. may be caused by expansion coil springs 35 cooperating with the solenoid coremountings to project them for movement of the gears 53, 33 into engagement with the gear 58. Selective operation of the solenoids-may be caused by a switching device which may include switches 33, 31. The

-- latter may comprise a common Z-shaped, sliding The normal position is contact switch member 33 mounted on the piston rod 43. Circuits 33, 13 connect the respective switches 33, 31 with the respective'solenoids 33, 34. A common "source of current 1| may be provided. It will now be clear close, and movement thereof rightward causes the switch 33 to close. Either switch remains closed while such movement continues. In neutral position of the piston 3, both switches are o en and the solenoids 33, 34 are deenergized. If the piston 43 moves to the left and closes the switch 31 the gear 33 disengages the gear 53; the

in Fi 2. The same shows particularly the face of an instrument 13, which may comprise a pointer 12 that turns with the pinion 23. Cooperating with the which the dial 15 maybe relatively and the dial 14 rotatable about the pointer. .This rotary dial 14 may be driven by the gear 53 and it turns clockwise. Normally the zero of the dial 14 coincides with that of the dial 15. Resetting of the dial 14 to such a position is desirable. Hence the casing of the instrument 13 may carry a pinion 13 actuable by a knob 11 and engaged with a gear portion 13 offthe dial 14. Also release .between the latter and the gear 53 must be provided, and this may be done by means of clutch element 13 frictionally engaging a ring element'connec'ted to the dial 14 and of which the gear portion 13 may form a. part. To avoid the resistance of the gear 13 when the clutch 13 is turning the dial 14, a conventional reciprocatory mounting may be used whereby the knob 11 may be moved to axially shift the gear 15 into or out of engagement with the gear 13.

one of disengagement.

axis of the one or the other Such movement that movement of thepiston rod 43 leftward causes the switch 31 to on of the data afforded by the device I3 is shown v inter are thedials 14 15 of stationary.

For use in very cold weather, the casing I I may be heated by any suitable thermostatic means, or heat may be applied directly to the Venturi tubes at the throat portions 28 thereof as indicated at 88. Preferably the heating means is remote from the expansion cones to prevent increased resistance of air by expansion due to heat. Hence the heating means is applied adjacent to the entrance portions 23 and it serves to prevent icing in the Pitot tubes.

A'typical use of the instrument will now be briefly described, for horizontal flight. With the dial 14 set so that its zero is at the zero of the stationary dial 15, the pointer 12 affords indica-. tions of altitude under normal conditions, as heretofore. If a sudden drop in barometric pressure occurs, this will be indicated by movement of the scale II clockwise, and will continue as long as that condition obtains and the aircraft continues to lose altitude due to decreased density and buoyancy of the atmosphere. Of course the pointer 12 moves to show a higher altitude, but the scale 14 shows that this is not so, and indicates the drop. Thus if the zero of scale I4 moves to numeral 2 on scale 15, the decrease in altitude is 2 units. If the pointer 12 is read against scale 14, then the result obtained is the approximate net or actual altitude. A highly beneficial result is obtained even if the pointer and the scale 14 are not thus coordinated. Although the airplane is in flight, the vertical component of relative air speed enters venturi 22 with the aid of the rectifier 21 and affects Pitot tube 38 causing piston 48 to move leftward so that switch 81 is closed and solenoid 84 is caused to retract gear 68 from gear 58, permitting the latter to be operated by the timing means, which, however, is regulated by governor 54. The speed of the latter may be increased by the cam 58 actuated by piston 48 in-proportion to the vertical energy of the air. The aneroid l3 actuates Pitot tube 38 to cause that energy to so affect the Pitot tube as to allow for varying air density, moving the tube upward at low altitudes and downward at high altitudes. The instant indication of the pointer I2 may jump considerably on a sudden drop in barometric pressure, while the dial 14 may move at a much slower rate. In that case the pointer cannot be read on the dial 18, but after a lapse of sufllcient time, or after the dial II has become stationary, indicating no further decrease in altitude, the pointer 12 may be read with significance On the dial H. Or the pilot may note the indication of the dial I4 against the dial I5, showing for example 2 units loss oialtitude. He may use his watch and find the time during which this loss has occurred and consult a chart prepared for his aircraft to thus obtain an indication of the drop of barometric pressure. Now he can gage the meaning of the reading of the pointer 12 on the dial 15. An additional means may be provided as will now be described so that the pilot may correct the altimeter for direct reading of the pointer for the new barometric pressure.

In Fig. 3 is shown an instrument 8! like that of Fig. 2, but having a third dial 82 rotatable by a central knob 83 and being otherwise stationary. This dial 82 may be calibrated for barometric pressure, or for units of altitude. From his chart, as above mentioned, the pilot may now move the altitude dial 82 so that the pointer 12 when read thereon indicates the true altitude. If desired, the knob 88 may carry indications 83a for barometric pressure and may be geared to the dial 82 to set the same for the correct altitude, but such mechanical connections between altitude and barometric scales are well known in the art and need not be shown herein.

If the dial I4 carries a barometric scale instead of an altitude scale, then the dial I5 may be made rotatable by a setting knob such as 83 geared thereto. In that case the knob 83 would be turned until the barometric scale 82 indicates the same reading as that of the dial 14, thus setting the scale I5 for a proper reading of the pointer. The indication of the scale 14 may be taken after a predetermined lapse of time, and during level flight. o

Continuing with the description of the mode of operation of the device ID, if the aircraft is climbing during a condition of sudden drop of barometric pressure, then the Pitot tube 3| cooperates to impose a pressure on the piston 48 tending to move the same toward the right so that the net effect is indicated by the indicator of Fig. 2.

If the aircraft is flying upward during normal barometric pressure, an indication may be caused by operation of the Pitot tube 3| alone, and the dial 14 may move counterclockwise. For this purpose the invention may serve as a climb indicator.

The reverse will also hold true if the aircraft is descending during normal barometric pressure, in which case only the Pitot tube 38 will be operated. The suction, if any, on the other Pitot tube may be negligible or the device may be designed so that it shall be extremely small.

It will be seen that a device embodying the invention may be designed for various conditions by proper selection of gear ratios and by suitable calibration of the scales.

In Fig. 4 is shown a modified drive for the pointer, 12 (which may be regarded as incorporated in Fig. 1) whereby the pointer may travel fast at low altitudes and relatively slowly at high altitudes, the scale divisions of the dial 15 being of correspondingly different sizes. The link it of Fig. l is connected to a small sector 85 of a gear, engaging a pinion 86 to the stem or pin 81' of which the pointer is aflixed. Secured to the sector 85 is a gear 88, engaging a relatively large sector 88 aflixed to the gear 86. The arrangement is such that the sector 85 is operative at the low altitudes on scale section 98, while sector 88 is free of the gear 88. As the last tooth of sector 85 is disengaging from the gear 86, the first tooth of sector 89 is engaging the gear 88 for continuity of operation without any lost motion. Then sector 89 operates at the high altitude section. Thus the use of a gear train is avoided and a single scale may have sections 88, 9| having larger subdivisions at low altitude for easier reading of they instrument, and yet permitting small scale divisions for a great altitude range.

I claim:

1. A device for indicating. dynamic energy in a stream of air including a Venturi tube, a Pitot tube having a pointed end concentric with the Venturi tube and extending into the expansion I cone of the latter and having its pointed end directed toward the throat of the venturi and bein movable relatively thereto, an aneroid controlling the movement of the Pitet tube, and an indicator responsive to the air pressure in the Pitot tube.

2. A device including a Venturi tube, means at the entrance thereof for avoiding eddy currents, including a streamlined element extending around the entrance, and having ,opposite surfaces creating like air pressures at said surfaces, said surfaces being at right angles to the Venturi tube, and a Pitot tube in the expansion cone of the Venturi tube having its operating end adjacent to the throat of the Venturi tube.

3. An indicating instrument having a scale ele-' sions, the gear means including two portions each based on one of said centers and each having a gear sector and a pinion secured thereto, the pinion of one portion being engageable with the sector of the other portion, while the pinion of the other portion disengages its sector:

4. A device for indicating dynamic energy in a stream of air including a pair of units, each unit comprising a Venturi tube and a Pitot tube having its pointed end concentric with the Venturi tube and extending into the expansion cone oi the latter with its pointed end directed toward the throat of the Venturi tube, and being axially movable relatively thereto, the units being so arranged relatively to each other that the pointed ends of the Pitot tubes extend in opposite directions, an aneroid, means whereby the aneroid causes movement in opposite directions of the Pitot' tubes, and an indicator responsive to the differential of the air pressures in the Pitot tubes.

VVELIAM NAIDA. 

